1. Field of the Invention
This invention relates to a method for preparing a substrate for a heat-generating device, which is suitable for providing a heat generating element required to repeat an intermittently heated state and non-heated state in extremely short cycles, such as an ink jet recording head or thermal head, and a method for preparing a heat-generating substrate having said heat-generating device and also a method for preparing an ink jet recording head.
2. Related Background Art
As the heat-generating device for various instruments such as ink jet recording heads or thermal heads, there have been widely used those having heat-generating resistance layers comprising various metals, alloys or inorganic compounds which generate heat by current passage and electrodes connected electrically to said heat-generating layers, all provided on a substrate.
As the substrate for arranging the heat-generating device thereon, there have been employed in the art those having insulating layers provided on a metallic base material, for the advantages of high heat dissipating characteristic, easy workability and low cost.
As such substrate, there have been known, for example, enamel substrates having enamel layers provided on metallic base materials, Alumite substrates having aluminum oxide coating provided on the surface according to an anodic oxidation method, organic film coating substrates having a film comprising an insulating organic compound coated on the metal surface, vapor deposition substrates having inorganic insulating material vapor deposited on the metal surface, or those with a constitution having two or more of these techniques combined.
Also, as a substrate using no metallic material, an Si substrate having a thermally oxidized product film thereon or an alumina substrate prepared by sintering alumina powder has been known.
Whereas, for the substrate for providing a heat-generating device required to repeat intermittently a heated state and a non-heated state in extremely short cycles, such as an jet recording head or thermal head, for example, various characteristics as shown below have been demanded.
a) To have a surface state such as surface roughness, etc. adequate for the formation of a heat generating device with good precision (for example, when the surface roughness approaches the thickness of the heat-generating device, desired resistance value cannot be obtained in some cases).
b) To have adequate heat-dissipating characteristics (for example, in the case of a substrate to be used for an ink jet recording head, if the substrate temperature becomes too high, bubbles are generated through lowering the solubility of dissolved gas in the ink within the head, which will hamper discharging ability in a thermal head, if heat-dissipating characteristics are bad, the so-called tailing phenomenon may occur).
c) To have heat-resistance to the extent sufficient to withstand the peak temperature of the heat-generating device.
d) To have insulating properties sufficient to withstand the driving voltage of the heat-generating device.
e) To be capable of easily forming a large device, when used for an instrument which is required to be made on a large scale.
f) When liquid such as ink, etc. or various materials to be in contact with the substrate or there is such possibility, to have resistance, for example, acid resistance or alkali resistance, to these.
Further, these characteristics are desirably obtained with low cost and high reliability.
However, no substrate satisfying sufficiently all of the above requisite characteristics has been found in the prior art.
For example, an enamel substrate can have formed thereon an enamel layer (which is an insulating layer) by coating a glassy material on the substrate surface by dipping, and therefore it is difficult to make the insulating layer thinner than a certain thickness, whereby good heat dissipating characteristics cannot be obtained.
On the other hand, in the case of an Alumite substrate, when aluminum oxide which becomes an insulating layer is coated by an anodic oxidation method, the aluminum oxide formed undergoes columnar crystal growth in the vertical direction relative to the substrate, whereby many voids may be sometimes formed so as to exhibit adequate heat dissipating characteristics. There was also a problem that the surface roughness after such anodic oxidation was too great. In order to obviate these problems, there may be used methods of applying sealing treatments and surface polishing, but these can cause new problems in that the number manufacturing steps becomes too large.
In Organic substrates, there was the problem that heat resistance was inferior.
Further, with vapor deposited substrates, defects such as pinholes in the vapor deposited layer are liable to be generated, and also good adhesiveness of the insulating layer to the substrate may not be obtained, whereby peel-off of the insulating layer may sometimes occur after prolonged usage. Thus, reliability was lacking, and also the preparation device was expensive, since a long time for preparation was required, whereby the results were not necessarily satisfactory in the aspect of cost.
Also, in substrates using metals as the base material, for formation of a good insulating layer on the base material, the surface must be subjected to mirror surface working by polishing, lapping, polish finishing, etc., and for this reason, the number of manufacturing steps is basically large, which was an obstacle against reduction in cost.
An alumina substrate can be prepared by sintering Al powder, with its surface being porous in nature, so that further lowering of surface roughness by surface polishing is limited, whereby it is required for obtaining preferable characteristic to apply further treatment such as a coating of a glaze layer. However, application of such treatment not only resulted in an increased number of steps, but there ensued sometimes the problem that heat dissipation was lowered.
On the other hand, an Si substrate having a thermally oxidized film, can satisfy the characteristics a)-d) and f) as described above, and therefore is more desirable in the aspect of performance from among the substrates of the prior art as described above. However, a problem remained in preparation of a substrate with a large area, and also working steps such as surface polishing, etc, are further required, and therefore there still remained room for further improvement also in the aspect of production cost.